The long term objective of this research is to investigate the molecularmechanism for the generation of the diversities of immune receptors. The V,(D), and J segments of the Ig and TCR genes are assembled by somatic recombination during the lymphoid differentiation. These recombination processes are mediated by the recombination signal sequences(Rss) and the V(D)J recombinase. To elucidate the molecular mechanisms of the V(D)J recombination, it is essential to characterize lymphoid-specific proteins that bind the Rss. We have cloned the cDNA for a protein, Rc, which is predominantly expressed in thymocytes, by the ability of Rc to bind the Rss. Subsequently, we have shown the Rc binds the kappa B motif and the Ig kappa chain gene enhancer as well. The aim of this project is to investigate the biological role of Rc in V(D)J recombination. The primary structure of Rc will be predicted from its CDNA and possible structural domains will be defined by comparing with proteins present in the databases. The information may shed light on how Rc can be involved in V(D)J recombination.